I don't have reproduction steps but I noticed this while someone was using Web Inspector in a WWDC lab. I think the popover also remains on screen on the wrong location if the layer it was attached to moved to a new spot.
<rdar://problem/14136942>
<rdar://problem/14136945>
Created attachment 212987 [details] Test case Attached a test case, steps to reproduce: 1. open the inspector 2. show the Styles sidebar 3. select the sole layer in the document 4. wait a bit for a second layer to appear (5s after load) At this point, notice how your existing layer has shifted down but the popover hasn't.
Created attachment 212988 [details] Patch
Comment on attachment 212988 [details] Patch Clearing flags on attachment: 212988 Committed r156673: <http://trac.webkit.org/changeset/156673>
All reviewed patches have been landed. Closing bug.